Current wireless communication services perform data transmission and reception using fixed bandwidths. Mobile communication systems maximize their performance through the arrangement of frequencies in cells and resources allocated to a specific band. A technology of transmitting and receiving signals using a fixed band is implemented through an invariant frequency range. A general method to provide a higher service quality (for example, a higher throughput or a greater number of users) while complying with current system protocols is to divide cells into smaller sections or to extend the existing system protocols according to the demand and then to install a new infrastructure.
Conventional methods of using frequency resources are divided into a technique based on fixed bandwidths and a technique based on scalable (or variable) bandwidths.
Systems that use the fixed bandwidth technique define protocols of services using various transmission/reception technologies suitable for specific bands. These systems are characterized in that they provide services based on fixed bands. So, if it is needed to change their protocols, it is necessary to change their entire service systems.
On the other hand, the scalable bandwidth technique, which is currently predominant, selectively applies various bandwidth options. For such scalable bandwidth protocols, it is easier to change bandwidths and to control the quality of service than fixed bandwidth protocols. However, in situations where actual services are provided, the scalable bandwidth system operates in the same manner as the fixed bandwidth system.
In summary, the scalable bandwidth system has an advantage in that no change is made to technologies employed in the system even when frequency bands have been widened or narrowed through the scalable bandwidth technique. The scalable bandwidth system can also change the quality of service without increasing the complexity of hardware since the employed technologies are not changed even if frequency bands are changed.
A new technique as an alternative to the above techniques is a Cognitive Radio (CR) technique. Mitola has suggested the CR technique in 1999 with an intention to efficiently use frequency bands. The CR technique is implemented basically based on Software-Defined Radio (SDR). The CR technique scans (or searches) frequency bands to select a spectrum that is not in use and sets the selected spectrum as a basic communication band. That is, the CR technique can perform spectrum sensing. According to the CR technique, the system can make a standalone determination as to whether to change the SDR architecture according to the type of a service found through the searching, to change the service type or the quality of service.
Taking into consideration both the fact that various wireless services are provided currently and the basic target concept of the CR technique, we can see that future wireless terminals will have an integrated form. That is, future wireless terminals are expected to operate according to the CR technique. The IEEE 802.22 currently employs the CR technique as a method to share TV bands to provide Wireless Regional Area Network (WRAN) services.
Some features of the CR technique are similar to those of some communication standards (or protocols) that use Industrial Scientific Medical (ISM) bands. Some standards that perform communication using the ISM bands provide a protocol to recognize frequency bands and to prevent collision in wireless (or radio) resources using a method called “coexistence”. The coexistence method also uses a variety of wireless resources through frequency detection and has common features with the CR technique.
In summary, if the communication methods are divided according to the frequency management techniques, they can be divided into the fixed bandwidth communication method, the scalable bandwidth communication method, and the CR communication method. Reference will now be made to the communication methods according to the various techniques with reference to the drawings.
First, reference is made to the fixed bandwidth communication method.
FIG. 1 illustrates use of wireless resources in the fixed bandwidth communication method.
Systems such as current mobile communication systems (CDMA, GSM, etc), wireless LAN (IEEE 802.11, HiperLAN, etc), or wireless PAN (IEEE 802.15) provide services using fixed bandwidths determined at an initial standardization stage. These bandwidths are some of the public bandwidths or the bandwidths, the use of frequencies of which has been authorized by the government. The fixed bandwidth communication method is characterized in that there is no increase or decrease in the frequency bandwidth with time. Thus, services provided in the fixed bandwidth are optimized for the bandwidth. That is, the fixed bandwidth communication method uses a predetermined bandwidth, regardless of the current amount of traffic.
Reference will now be made to the scalable bandwidth communication method.
Services using scalable bandwidths can be divided into two types. Services of the first type are provided in the case where the terminal uses a variable bandwidth while the base station uses a constant bandwidth. Services of the second type are provided in the case where both the base station and the terminal use variable bandwidths.
An example of the first type is shown in FIG. 2. The example of FIG. 2 may be a service of the IEEE 802.16 or 802.20 protocol using OFDM. The example of FIG. 2 may also be a service of the 3GPP Long Term Evolution (LTE) or the like. In the CDMA mode, the example of FIG. 2 may be a service of Evolution Data Only (EV-DO) or Evolution Data and Voice (EV-DV), which is a method of grouping and allocating channels to terminals. In the example of FIG. 2, the total bandwidth used by the base station is fixed and the base station allocates a specific bandwidth to the terminal. The terminal receives services through the allocated bandwidth. The bandwidth used by the base station is determined during installation of the system.
Reference will now be made to the scalable bandwidth communication method that incorporates some features of the CR technique.
FIG. 3 illustrates a method of using wireless (or radio) resources in the scalable bandwidth communication method that incorporates some features of the CR technique. As shown in FIG. 3, the bandwidth through which the base station provides services may vary with time. The example of FIG. 3 may be that of the IEEE 802.22 protocol. The IEEE 802.22 protocol is a service model created by incorporating the features of the CR technique. That is, an available frequency band is detected in each time unit and the base station extends its services within the available bandwidth. Accordingly, terminals of the IEEE 802.22 standard (or protocol) must be able to accommodate all changing bandwidths. In the IEEE 802.22 standard, Wireless Regional Area Network (WRAN) services are provided by sharing TV bands and each service unit is provided using channels that are not used in other services, basically according to a channel combination/split method. That is, when the base station detects a TV channel that is not in use, the base station uses that TV channel to provide a WRAN service. If consecutive TV channels are available within the range specified in the standard, the channels are grouped to be used as a single band and it is possible to provide services using the entirety of the band. The terminal must recognize all such states of the channels of the base station and increase its receiving capability accordingly.
Reference will now be made to the CR technique. The CR technique is characterized in that it is not limited to a specific frequency management method. That is, the CR technique is characterized in that the configuration of a terminal changes according to frequency resources in order to more efficiently use the current spectrum (i.e., the frequency resources).
FIG. 4 illustrates how a terminal according to the CR technique (hereinafter referred to as a “CR terminal”) uses wireless resources when some of the wireless resources are not in use.
As shown in FIG. 4, the CR terminal freely examines and selects a spectrum. That is, the CR terminal monitors spectrums as shown in FIG. 4 and thus can detect that wireless resources of bands 401 to 406 are not in use. Accordingly, first, the CR terminal can receive a general CR service through bands shown with a name “Conventional service with CR” in the bands 401 and 402. The CR terminal can also create a new service through the bands 401 and 402.
If the CR terminal detects that the wireless resources of the bands 401 and 402 are not available any longer after time “t1”, the CR terminal can receive the service or provide a new service through the wireless resources of the band 403 after time “t1”. If the wireless resources of the band 403 are not available any longer after time “t2”, the CR terminal can select the wireless resources of the band 406 to continuously receive or provide the service after time “t2” as shown in FIG. 4.
If there are spectrum bands to be monitored and a region not in use is detected in the bands, the CR terminal receives a communication service that is provided according to the CR technique through the region.
Of course, the service provided may be a fixed bandwidth service and may also be a scalable bandwidth service. The CR technique is characterized in that, because frequency resources that are in use change with time in contrast to the conventional services, it requires both a protocol to manage the change of the frequency resources and a process of learning the frequency resources. An example of the current standard having the characteristics of the CR technique is an IEEE 802.22 WRAN system.
One feature of the CR technique is that it freely uses frequency bands, compared to other techniques. In the scalable bandwidth communication method, bandwidths available in the communication system are preset although a bandwidth used changes with time and communication is performed while the used bandwidth changes within the preset bandwidths. However, the CR technique freely scans frequency bands without the preset restriction. The CR technique is also characterized in that, if an available band is detected, a service is received or created through the detected band.
Communication protocols using the fixed bandwidth technique and the scalable bandwidth technique have the following problems.
The current system needs to be modified when there is a demand of consumers in the future. To meet the demand of consumers, it is necessary to create a new standard and to provide a new system. In other words, systems using fixed bandwidths and systems using scalable bandwidths must always change their protocols at the desires of consumers. However, since it is difficult to fully meet the desires of consumers through a single service, various types of services are provided, thereby reducing the spectrum efficiency. Particularly, the use of spectrums locally and temporally changes at limited demands of users. That is, there is a problem in that the use of spectrums is inefficient when there are such limited demands of users. Thus, wireless terminals will evolve based on the CR technique in order to meet changing desires of users and to accommodate a variety of communication techniques.
However, no one has suggested a band utilization method and a communication method for the CR technique. The current discussions focus on how reconfiguration to recognize and determine frequency environments is implemented in an SDR terminal which accommodates the conventional type of wireless systems without change. Although this CR operation scenario has an advantage in that it integrates all wireless terminals, it has a problem in that it fails to consider an evolution toward efficient use of spectrums while fully satisfying changing desires of users.